Method for producing ceramic-based components

ABSTRACT

A method of heat treating ceramic-based electronic components by providing a furnace fixture adapted to support the ceramic-based electronic components which is made from a substrate selected from the group consisting of silicon carbide (SiC), cordierite (2MgO.2Al2O 3 .5SiO 2 ), mullite (3Al 2  O 3 .2SiO 2 ), stabilized zirconia, magnesium oxide (MgO) and alumina (Al 2  O 3 ) containing a glassy bond phase. A cladding layer of zirconia or magnesia is then deposited on the furnace fixture substrate by plasma deposition. The ceramic-based electronic component to be fired is placed on the zirconia-coated substrate; and heated to a desired temperature to heat treat the component.

This application is a continuation-in-part of U.S. Ser. No. 075,683filed Jun. 11, 1993, now U.S. Pat. No. 5,336,453.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for producingceramic-based electronic and other components, and more particularly toa particular combination of ceramic compositions useful for fixtures forheat treating such components.

2. Description of Related Art

Components in electronic circuitry utilize ceramic materials for bothsubstrates and semiconductor packages. However, the most common type ofceramic-based electronic components for which the present invention isuseful in heat treating are ceramic capacitors, resistors, thermistorsor the like which are typically made up of multiple layers of oxide ornonoxide ceramics having suitable dielectric properties. Common sizesare 0.08×0.05 in., 0.125×0.063 in. and 0.5×0.225 in. Multilayer ceramicsare also used as substrates for integrated circuit packages.Alumina-based ceramics are widely employed, as well as mullite (3Al₂O₃.2SiO₂), beryllia (BeO), aluminum nitride (AlN) and various other wellknown glass-ceramic materials, depending on the dielectric constant,coefficient of thermal expansion, and other properties desired.Different classifications for ceramic dielectric materials are Class Idielectrics with low k (dielectric constant) values made by mixingmagnesium titanate with calcium titanate; Class II dielectrics with highk values (also known as ferroelectrics) based on barium titanate,optionally with additions of barium stanate, barium zirconate ormagnesium titanate; and Class III dielectrics. Other ceramic materialsused in electronic applications include magnesia; nickel manganates(NiO.MnO₂); zirconia (ZrO₂); yttria (Y₂ O₃); lead compounds such as leadoxide (PbO), lead non-oxides, lead zirconium titanates, lead titanates,and lead metaniobates; beryllium compounds such as BeO; ferrous oxidecompounds (e.g., magnetic and non-magnetic FeO compounds, includingthose in mixture or compound with Zn and/or Mn) and ferrites. Ferritesare a well known class of ceramics having the spinel cubic structure ofthe general formula XFe₂ O₄, where X may represent Ba, Zn, CD, Cu, Mg,Co, Ni, Mn, Fe or a mixture of these or other ions.

In processing such ceramic-based electronic components, the parts in the"green" state are fired one or more times to temperatures ofapproximately 1000° C.-1700° C. and higher, more typically 1100°C.-1500° C., to achieve vitrification, sintering and/or densification.Total cycle times for heat treatment are typically eight (8) hours orlonger, although shorter times may be used where there is only a smallmass of product. Firing may be done under a vacuum or protectiveatmosphere but is typically done in air. Standard type furnaces or kilnsemployed in the industry are typically either the pusher or tunnel typeand the periodic or batch type.

The devices or fixtures by which the ceramic components are physicallysupported during the firing process are generally termed furnace or kilnfurniture. Other well known nomenclature is utilized for variousconfigurations and types of fixtures such as saggers, setters, andplates, and varieties of substrates with rails or sidewalls. Processesused for manufacturing prior art monolithic furnace fixtures includepress cast molding, powder roll compaction, tape casting, slip castingor extrusion of the green ceramics to the desired shape, followed byfiring of these materials in the range of temperatures given previously.A wide variety of ceramic materials have been employed such as theaforementioned and other alumina and alumina-based ceramics, as well aszirconia and magnesia. In some instances, powdered forms of theseceramics have been applied to furnace fixtures either as dry powders oraqueous washes which are then dried to leave a powder residue, toprevent sticking of the components to the fixture surface.

Although the prior art methods of using these monolithic furnacefixtures have not changed dramatically over the years, there has been along sought need to reduce furnace time and associated energy costs tomaximize productivity in processing ceramic-based electronic components.With some types of fixture materials, especially those which have lowreactivity with typical ceramics used in electronics, this has beendifficult because of the relatively thick fixture cross sectionsnecessitated for purposes of maintaining strength and thermal shockresistance. In some instances, the fixture panels had high porosity anda rough surface, and were not considered mechanically suitable for usein thin, large panels which are desirable for maximizing the number ofcomponents which may be placed in the furnace. The result has been thata relatively large amount of furnace heat goes to heating the fixturesthemselves, which not only costs more fuel but also penalizes theprocess by requiring longer heat up and cool down time for the combinedmass of fixtures and electronic components. Ceramic materials which havegreater strength, can be easily processed to flatness and otherdimensional parameters, and can withstand cyclic exposure to hightemperature firing such as alumina do not have the degree of chemicalinertness needed for processing many of the variety of ceramics used inelectronics, and therefore have only limited potential for use.

Similar problems have been encountered in firing other ceramiccomponents from the green state. Other components include those madefrom zirconium oxide (ZrO2), such as oxygen sensors used to regulateinternal combustion engines.

Bearing in mind the problems and deficiencies of the prior art, it istherefore an object of the present invention to provide a process forheat treating ceramic-based electronic and other components whichreduces the time and energy required to fire the components, while atthe same time providing a surface for contacting the component which isrelatively inert so as to avoid chemical contamination of the ceramicsemployed in the components.

It is another object of the present invention to provide furnacefixtures for processing ceramic-based electronic and other componentswhich have a relatively thin cross section while having a high degree ofstrength and resistance to thermal cycles at the temperatures andconditions employed in heat treating such components.

It is a further object of the present invention to provide furnacefixtures for processing ceramic-based electronic and other componentswhich may be produced to close tolerances for flatness and otherdimensional parameters.

It is yet another object of the present invention to provide a processfor heat treating ceramic-based electronic and other components in whichthe furnace fixtures eliminate sticking of the components to the fixturesurface and have a long working life.

It is a further object of the present invention to provide furnacefixtures for processing ceramic-based electronic and other components inwhich the total volume of fixture material is reduced and the volume offurnace space which is available for components to be heat treated isincreased.

SUMMARY OF THE INVENTION

The above and other objects, which will be apparent to those skilled inthe art, are achieved in the present invention which in one aspectrelates to a method of heat treating ceramic-based electronic and othercomponents by providing a furnace fixture adapted to support theceramic-based electronic components which is made from a substrateselected from the group consisting of silicon carbide (SiC), cordierite(2MgO.2Al2O₃.5SiO₂), mullite (3Al₂ O₃.2SiO₂), stabilized zirconia,magnesium oxide (MgO) and alumina (Al₂ O₃) containing a glassy bondphase. A cladding layer of zirconia or magnesia is then deposited on thefurnace fixture substrate by plasma deposition. The ceramic-basedcomponent to be fired is placed on the zirconia-or magnesia-coatedsubstrate and heated to a desired temperature to heat treat thecomponent.

In another aspect, the invention relates to an apparatus or system forheat treating ceramic-based electronic components comprising a furnaceand a furnace fixture having a substrate selected from the groupconsisting of silicon carbide (SiC), cordierite (2MgO.2Al2O₃.5SiO₂),mullite (3Al₂ O₃.2SiO₂), stabilized zirconia, magnesium oxide (MgO) andalumina containing a glassy bond phase. The substrate is clad by abonded layer of plasma-deposited zirconia or magnesia, and thezirconia-or magnesia-clad fixture substrate supports the ceramic-basedcomponent for firing.

In a further aspect, the invention relates to a fixture for heattreating ceramic based components comprising a base having an uppersurface for supporting the ceramic based component, wherein the base hasa substrate selected from the group consisting of silicon carbide (SiC),cordierite (2MgO.2Al2O₃.5SiO₂), mullite (3Al₂ O₃.2SiO₂), stabilizedzirconia, magnesium oxide (MgO) and alumina containing a glassy bondphase. The base substrate is clad on at least a portion of its uppersurface by an impermeable top layer of plasma-deposited zirconia ormagnesia. A pair of integral side rails on opposite ends of said baseextend above the upper surface and are spaced and have a height abovethe top surface of the base greater than the width and height,respectively, of the ceramic-based electronic component to be heattreated on the zirconia- or magnesia-clad portion of the fixture.

The preferred substrate comprises a thin plate of less than 0.100 in.made from alpha alumina in an amount no greater than about 98% by weightof the substrate and at least about 2% by weight of an oxide of siliconor an alkali or alkaline earth metal, or combinations thereof. Thecladding preferably comprises a smooth, impervious layer of stabilizedcubic zirconia or magnesium oxide in a thickness of 0.0001-0.010 in.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of the furnace apparatus of thepresent invention employing zirconia-or magnesia-clad furnace fixturessupporting ceramic-based electronic components for heat treatment.

FIG. 2 is a perspective view of a zirconia- or magnesia-clad furnacefixture of FIG. 1 supporting ceramic-based electronic components.

FIG. 3a is a cross-sectional view through a first embodiment of thefurnace fixture of FIG. 2 showing the zirconia or magnesia coating layeron all sides of the fixture.

FIG. 3b is a cross-sectional view through a second embodiment of thefurnace fixture of FIG. 2 showing the zirconia or magnesia coating layeron only the upper component-supporting surface of the fixture.

FIG. 4 is a perspective view of another zirconia- or magnesia-cladfurnace fixture for supporting ceramic-based electronic components whichemploys separate spacer rails.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The most common type of ceramic-based component for which the presentinvention is useful in heat treating are electronic components such asceramic capacitors which are typically made up of multiple layers ofceramics having suitable dielectric properties, although the inventionmay be utilized for processing any of the aforementioned types ofelectronic and other components and ceramic materials previouslydiscussed in the background section of this application. The presentinvention is based on the discovery that improved furnace fixtures forheat treating ceramic-based electronic components, also known as "kilnfurniture", may be produced by depositing a solid cladding layer ofzirconia or magnesia by plasma deposition in air over certain ceramicsubstrates. Such furniture fixtures are found to possess higher strengthand better protection of the ceramic components (preventing sticking andcontamination thereof) in smaller cross sections, which results infaster furnace and component heat-up rates and closer packing ofcomponents in the furnace, and which ultimately reduces the unit energyrequired to heat treat the ceramic-based electronic components.

For purposes of the present invention, the furniture fixture materialswhich have been found to be most desirable as substrates for thezirconia or magnesia coating are: 1) silicon carbide (SiC); 2)cordierite (2MgO.2Al₂ O₃.5SiO₂); 3) mullite (3Al₂ O₃.2SiO₂); 4) zirconiastabilized with calcia, magnesia or yttria; 5) magnesium oxide (MgO)and, preferably, 6) alumina (Al₂ O₃) having alpha alumina crystals boundby a bond phase of silica (SiO₂) and/or other glassy oxides such asmagnesia (MgO), calcia (CaO), sodium monoxide (Na₂ O), ferric oxide (Fe₂O₃), zirconia (ZrO₂), or combinations of the above. The preferredalumina containing the glassy bond phase contains silica and has acomposition of no greater than about 98% Al₂ O₃, and at least about 2%silica and/or the other aforementioned oxides, and more preferably has acomposition of 96% Al₂ O₃ and 2.5-3.0% SiO₂. (Unless otherwise noted,all references herein to composition percentages are in weight percentof the total.) Higher amounts of silica, up to about 25%, in thepreferred alumina substrate composition have been shown to provide goodbonding with the plasma deposited zirconia or magnesia, with no otheradverse effects on manufacturing, operation and use of the invention.Additionally, zirconia (ZrO₂) may be added as a component to thepreferred alumina containing the glassy bond phase to provide zirconiatoughened alumina , also known as "ZTA", which may be employed as asubstrate material for the furnace fixtures of the present invention.The addition of unstabilized zirconia provides toughness for resistanceto shock in extended thermal cycles.

Processes used for manufacturing the furnace fixtures include molding,powder roll compaction, tape casting, slip casting or extrusion of thegreen ceramics to the desired plate-like shape, followed by firing ofthese materials, as described previously. These aforementioned preferredfixture substrate materials generally provide strong, thermally shockresistant platforms for the electronic components at base sectionthickness of less than 0.100 in., preferably 0.040-0.060 in., and atlengths and widths of 3-6 in. When stacked and separated by spacers,these relatively thin fixture plates maximize the volume availableinside the furnace for the ceramic-based electronics productsthemselves, which can have thicknesses up to 0.025 in. and higher.Naturally, if desired for special applications, the fixture panels maybe manufactured and used in the higher thickness employed in the priorart, typically up to 0.500 in. However, unlike the previously utilizedmonolithic panels of zirconia which typically required a thickness over0.100 and up to 0.400 in. or more, and had high porosity and a roughsurface, the substrate panels to be utilized in the present inventionhave relatively dense, smooth surfaces and are mechanically suitable foruse in thin, large panels.

The zirconia to be plasma sprayed as the coating or cladding over theaforementioned fixture substrate materials is preferably stabilized to acubic matrix by the addition of oxide stabilizers such as magnesia(MgO), calcia (CaO), yttria (Y₂ O₃), lanthana (La₂ O₃) and Ce₂ O₃. Thezirconia to be plasma deposited is more preferably stabilized withmagnesia and has a composition of approximately 76% ZrO₂ (unstabilized)and 24% MgO, although calcia- and/or yttria-stabilized zirconia are alsobelieved especially useful. In the case where the zirconia is plasmasprayed over a zirconia substrate (manufactured as describedpreviously), the zirconia coating contrasts with the substrate by itssubstantially increased density and smoother surface, as-deposited. Thepreferred particle size of the zirconia is 140-325 U.S. Mesh, althoughother particle sizes may be utilized with different applicationequipment. As indicated, the stabilized zirconia is deposited on theceramic furnace fixture substrate by plasma deposition, which is a wellknown process utilized in other industries. The plasma deposition maytake place in air or in a protective or inert atmosphere. Prior toapplying the plasma spray deposition, it is desirable to prepare thesurface of the substrate by grit blasting to clean and roughen thesurface to promote adhesion and bounding of the solid zirconia layer.Plasma deposition takes place by ionizing the carrier gas, addingzirconia powder and applying it by conventional plasma gun to a desiredthickness inches at a predetermined traverse and feed rates. While anysuitable thickness of zirconia may be utilized, such as up to 0.025 inor more, typically the zirconia topcoat layer may range front about0.0001 to about 0.0100 in., preferably from about 0.0005 to about0.035-0.0040 in., most preferably 0.0015 in. As-deposited the preferablystabilized zirconia provides a thin yet solid, smooth, essentially porefree, impermeable coating over desired areas of the fixture substratematerial coming in contact with the ceramic components. The relativelyinert zirconia cladding is especially useful in preventing contaminationof the electronic components from the silica and the alumina in thesilicon carbide, cordierite, mullite and preferred alumina substrates.For additional smoothness, the surface may be sanded with a lightabrasive after plasma deposition.

Magnesia may be applied by plasma deposition in the same manner asdescribed herein for zirconia. As used herein, "magnesia" as a claddingincludes not only the compound magnesium oxide (MgO), but also includesspinel, the solid state reaction between magnesium oxide (MgO) andalumina (Al₂ O₃), also known as MgO.Al₂ O₃ or MgAl₂ O₄. Spinel can beadjusted for a wide range of MgO Al₂ O₃ ratios, although a weight ratioof 1:3 is preferred. Magnesium oxide (MgO) in powder form preferablecontains up to about 8% yttria (Y₂ O₃) and may contain minor or traceamounts of SiO₂, Al₂ O₃, Fe₂ O₃, Na₂ O or other compounds as present incommercially available product. Similar cladding layer thicknesses maybe deposited, most preferably in the range of about 0.003-0.010 in., toyield the thin, solid, smooth and impermeable coating. Where magnesia isapplied over a magnesium oxide (MgO) substrate, for example, theplasma-deposited coating has greater density and impermeability, andfewer impurities, than may be manufactured in the substrate.

The method and apparatus provided by the present invention stands incontrast with the prior art in which unstabilized or essentially purezirconia or alumina flour was applied in either dry form or a wash overthe surface of the monolithic ceramic materials described previously forfurnace fixtures. In such prior art, the zirconia and alumina powdersadded nothing to the strength or properties of the furnace fixtures, andrequired reapplication after every use.

In operation, the ceramic-based electronic or other components aretypically spaced single height on the zirconia or magnesia-clad surfaceof the fixtures produced by the process of the present invention. Thesefixtures are then stacked one upon the other utilizing spacers, whichmay be integral rails on the fixtures or separate pieces. Preferably,the spacers themselves are zirconia or magnesia clad to reduce stickingbetween adjacent pieces. The stacked components are then placed insidethe furnace and heated to the firing temperature for a desired time. Theheat treating temperatures of approximately 1000° C.-1700° C. used tofire the ceramic components, while sometimes being within thevitrification range of the particular ceramic, is below that at whichthe components become substantially molten. The particular combinationof a relatively thin plasma deposited zirconia or magnesia layer on asubstrate of alumina having a glassy bond phase results in a heatingrate that is considerably faster than if the same thickness of zirconiaor magnesia is utilized as the furniture fixture. At the thicknessesdescribed herein, the zirconia coated substrate of alumina having theglassy bond phase will have a heating rate that is approximately 14times higher than that of a monolithic zirconia plate of similarthickness. Where a zirconia-clad alumina plate of 0.060 in. thicknessreplaces a prior art plate of zirconia of 0.240 in. thickness, theheating rate will be more than 200 times faster.

While prior art fixtures such as monolithic zirconia in the relativelythick sections employed had good thermal shock resistance, believed tobe due in part to the porosity present which arrests crack propagation,the alumina containing the glassy bond phase preferred as the fixturesubstrate of the present invention is believed to have comparable orbetter properties in this regard, despite having typically thinner(0.060 in.) sections and higher density. Furthermore, the bonding of theplasma-deposited zirconia or magnesia to the substrates to be employedin the present invention is extremely strong so that a long working lifeof the zirconia or magnesia-clad fixtures is expected. While not wishingto be bound by theory, it is believed that the presence of the thinglassy layers at the boundary of the alpha alumina crystals of thepreferred composition of the present invention results in high thermalshock resistance, and that the thermally induced interface stressesbetween the zirconia or magnesia coating and alumina substrate arenegligible as a practical matter. Additionally, it is believed thatthese characteristics of the alumina containing a glassy bond phaseresults in a stronger bond between the zirconia or magnesia layer andthe alumina substrate. Bond strength of the zirconia is expected to beenhanced over time because of solid state diffusion expected along thezirconia/substrate interface. The possible presence of a spinel,generically designated as a structural group: XY₂ O₄, and more commonlyknown as the mineral MgO.Al₂ O₃ (or MgAl₂ O₄), is believed to contributeto the favorable characteristics of the invention described herein.

With reference to the drawings, which are not necessarily shown toscale, FIG. 1 is a side elevational view of the furnace apparatus of thepresent invention employing zirconia-clad furnace fixtures supportingceramic-based electronic components for heat treatment. Furnace 10 has athermally insulative lining 11 and a base plate 12 of any desiredrefractory material for supporting the mass of fixtures and components.A plurality of zirconia- or magnesia-clad fixtures or setters 14 havingintegral side rails 16 are stacked upon each other within furnace 10.Disposed upon the fixture upper supporting surfaces 18 are a pluralityof ceramic-based electronic components 20, which due to the greaterheight of rails 16, have sufficient space above and to the sides toprevent contact between one another and the lower surface of the fixtureabove. At least the flat upper supporting surface 18 of each fixture 14is zirconia or magnesia-clad to prevent chemical contamination of thecomponents 20 by the fixture substrate material of the type describedpreviously. As shown more clearly in FIG. 2, for maximum heatingefficiency, the supporting surface thickness "a" of the fixture 14 iskept to a minimum, preferably below 0.100 in., more preferably0.040-0.060 in., so as to maximize the mass of components 20a and 20bcontained in a given internal volume of the furnace. The typical widthand depth dimensions of the fixtures, on the order of 4-6 in., makesflatness of the fixture important at such thin sections.

Cross-sectional views of fixture 14 are shown in FIGS. 3a and 3b. InFIG. 3a, the zirconia or magnesia 22a is shown deposited on thesupporting surface 18a and all other sides of the fixture, whereas inFIG. 3b the zirconia or magnesia 22b is shown deposited on only thesupporting surface 18b, leaving the fixture substrate material exposedon the remaining sides. For maximum performance and life, all sides ofthe fixture substrate should be zirconia- or magnesia-clad.

An alternate configuration of a furnace fixture is depicted in FIG. 4 inwhich a flat, rectangular, zirconia-or magnesia-clad fixture plate 24supports components 20a and 20b on its supporting surface 18. Plate 24employs separate rails or spacers 26 of 0.250 in. thickness to separateand support adjacent levels of fixtures. The ceramic-based electroniccomponents generally have a thickness of under 0.250 in., but thickerspacers or rails are used for larger components. Fixtures of the typeshown in FIGS. 2 and 4 may be stacked up to 30-50 levels high in atypical furnace having interior dimensions of 18 in.×18 in.×18 in.

EXAMPLE

As a non-limiting example of the present invention, a furnace fixturesubstrate, or "setter", comprised of a silica-containing alumina has atypical analysis as follows (in weight percent):

    ______________________________________                                        Al.sub.2 O.sub.3   96                                                         SiO.sub.2          2.5-3.0                                                    MgO                0.75-1.0                                                   CaO                0.10-0.25                                                  Na.sub.2 O         0.05-0.10 max.                                             Fe.sub.2 O.sub.3   0.03-0.05                                                  ZrO.sub.2          0-0.05                                                     ______________________________________                                    

This alumina has a glassy bond phase between alpha alumina crystals andis fabricated by casting or extrusion to a size of 4.5×4.5 in. andthickness of 0.060 in. The surface of the setter is then grit blastedwith no. 220 aluminum oxide grit at an air pressure of 65 to 70 psi at agun distance of 4 to 5 inches and angle of 90° to obtain an even mattefinish, with concentration on edge areas to provide good bondingproperties for the zirconia coating. Avoiding contact with the skin, thesetter is then ready for plasma deposition of the zirconia powder,which, without further protection, should be performed within two (2)hours of surface preparation for best results.

The zirconia powder utilized is magnesia stabilized, i.e., with acomposition of 76% ZrO₂ and 24% MgO. For applying the plasma coating, aMetco plasma system may be utilized in which the zirconia powder isdried by preheating to 170° F.±25° F. and mixing for 15 minutes. Thesetter is mounted on a turntable and rotated during deposition. Plasmaspraying is done at a power of 1000 Kw (70 volts DC, 500 amps) at apressure of 100 psig and feed rate of 5 pph in an air atmosphere. Thestabilized zirconia is deposited by the high energy plasma spray in onepass to a uniform thickness of approximately 0.0015 in., and within arange of 0.001-0.0035 in. The plasma coated alumina substrate is thenrubbed lightly with 200 grit sandpaper to produce a smooth finish.

A ceramic-based electronic component is then placed on the plasmacoated, zirconia-clad alumina setter and inserted into a conventionalheat treating furnace and heated to a temperature of 1100°-1400° C. inair for 2 hours.

Likewise, a magnesia-clad setter utilizing the aforedescribedcompositions of magnesia powder may be made and used to fire aceramic-based component in a similar manner as described above.

The finished plasma sprayed zirconia or magnesia coating on the furnacefixture of alumina or other substrate allows users to benefit by theresistance of the zirconia or magnesia cladding layer to reaction andcontamination which allows extended time between replacement andelimination or lessening of sticking problems with the ceramic-basedcomponents. The system of the present invention has been tested andproven reliable for many electronic and non-electronic components. Thezirconia cladding has been found to be especially useful when firingferrite, titanite, nickel manganate (NiO.MnO₂), zirconia and yttriaceramic components. The titanates include sensitive barium titanate andmagnesium titanate electronic components. The magnesia cladding isuseful in firing lead compounds (e.g., lead oxide, lead non-oxides, leadzirconium titanates, lead titanates, lead metaniobates), ferrous oxidecompounds (e.g., non-magnetic compounds, including those in mixture orcompound with Zn and/or Mn) and beryllium compounds (e.g., BeO). Thinnercross sections of the composite zirconia- or magnesia-clad substrate maybe utilized than with monolithic zirconia or magnesia and with a greaterflatness for increased furnace capacity. As compared to monolithiczirconia or magnesia, the increased thermal conductivity of alumina bodycombined with the overall lower mass will yield a faster ramp up anddown from firing temperatures.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above constructions withoutdeparting from the spirit and scope of the invention, it is intendedthat all matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

While the invention has been illustrated and described in what areconsidered to be the most practical and preferred embodiments, it willbe recognized that many variations are possible and come within thespirit and scope thereof, the appended claims therefore being entitledto a full range of equivalents.

Thus, having described the invention, what is claimed is:
 1. A method ofheat treating ceramic-based components selected from the groupconsisting of titanates, ferrites, nickel manganate, zirconia, yttria,lead-containing compounds and beryllium-containing compounds, saidmethod comprising the steps of:a) providing a furnace fixture adapted tosupport said ceramic-based components comprising a substrate selectedfrom the group consisting of silicon carbide (SiC), cordierite(2MgO.2Al₂ O₃.5SiO₂), mullite (3Al₂ O₃.2SiO₂), stabilized zirconia,magnesium oxide (MgO) and alumina containing a glassy bond phase, saidsubstrate having deposited on at least a portion of a surface thereof atop cladding layer of plasma-deposited zirconia or magnesia, saidcladding layer being substantially inert to said ceramic-basedcomponents to prevent contamination thereof; b) providing saidceramic-based component; c) placing said ceramic-based component on thezirconia- or magnesia-coated portion of said substrate; and d) firingsaid ceramic-based component and zirconia-or magnesia-clad substrate toa desired temperature to heat treat said ceramic-based component.
 2. Themethod of claim 1 wherein said substrate has deposited on at least aportion of a surface thereof a top cladding layer of plasma-depositedzirconia.
 3. The method of claim of claim 2 wherein said substratecomprises alumina in an amount no greater than about 98% by weight ofsaid substrate and at least about 2% by weight of an oxide of silicon oran oxide of an alkali or alkaline earth metal, or combinations thereof.4. The method of claim 2 wherein said substrate comprises siliconcarbide (SiC).
 5. The method of claim 2 wherein said substrate comprisesstabilized zirconia or magnesium oxide (MgO).
 6. The method of claim 2wherein said substrate comprises cordierite (2MgO.2Al2O₃.5SiO₂).
 7. Themethod of claim 2 wherein said substrate comprises mullite (3Al₂O₃.2SiO₂).
 8. The method of claim 2 wherein said cladding layer consistsessentially of zirconia.
 9. The method of claim 1 wherein said substratehas deposited on at least a portion of a surface thereof a top claddinglayer of plasma-deposited magnesia.
 10. The method of claim 9 whereinsaid substrate comprises alumina in an amount no greater than about 98%by weight of said substrate and at least about 2% by weight of an oxideof silicon or an alkali or alkaline earth metal, or combinationsthereof.
 11. The method of claim 9 wherein said substrate comprisessilicon carbide (SiC).
 12. The method of claim 9 wherein said substratecomprises stabilized zirconia or magnesium oxide (MgO).
 13. The methodof claim 9 wherein said substrate comprises cordierite(2MgO.2Al2O₃.5SiO₂).
 14. The method of claim 9 wherein said substratecomprises mullite (3Al₂ O₃.2SiO₂).
 15. A method of heat treatingceramic-based components selected from the group consisting oftitanates, ferrites, nickel manganate, zirconia, yttria, lead-containingcompounds and beryllium-containing compounds, said method comprising thesteps of:a) providing a furnace fixture adapted to support saidceramic-based components comprising a substrate of alumina containing aglassy bond phase, said substrate having deposited on at least a portionof a surface thereof a top cladding layer of plasma-deposited zirconia,said cladding layer being substantially inert to said ceramic-basedcomponents to prevent contamination thereof; b) providing saidceramic-based component; c) placing said ceramic-based component on thezirconia-coated portion of said substrate; and d) firing saidceramic-based component and zirconia-clad substrate to a temperature ofat least 1000° C. to heat treat said ceramic-based component.
 16. Themethod of claim 15 wherein said substrate comprises alumina in an amountno greater than about 98% by weight of said substrate and at least about2% by weight of an oxide of silicon or an oxide of an alkali or alkalineearth metal, or combinations thereof.
 17. The method of claim 15 whereinsaid cladding layer consists essentially of zirconia.